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Gestures on Apple iPad Control Nano-Tweezers

R. Colin Johnson | Date: 03-11-11 | Comments

Using an iPad's touch screen allows intuitive gesture control of holographic optical tweezers so that even a novice can manipulate microscopic scientific samples like a trained technician.

The iPad is becoming a scientific remote control, allowing intuitive multitouch gestures to more easily control complex manipulations using holographic optical tweezers.

Optical tweezers use laser beams to physically hold microscopic objects�from living cells to nanoparticles�allowing operators to rotate, zoom into and closely inspect microscopic objects using the same intuitive gestures used to manipulate the macroscopic world. (Try out a simulated version of iTweezers called iHologram that allows you to manipulate virtual nanoparticles on your iPhone or iPad.)

Holographic optical tweezers use a spatial light modulator (SLM) to steer and multiplex a laser beam to allow multiple particles to be interactively manipulated in three dimensions. Giving human operators enough variable parameters to control them, however, has been a challenge. Multi-axis joysticks and motion-capture technology have been developed to partially mitigate the problem, but now researchers at the University of Glasgow and the University of Bristol (U.K.) say that an iPad's multitouch gesture interface allows much more intuitive control of the necessary multi-axis manipulations.

For the iPad's 10-inch capacitive touch screen, the researchers' iPad app can simultaneously control as many as 11 particles, and wirelessly relay the necessary control parameters from the iPad to the PC actually controlling the optical tweezers. Intuitive gestures were crafted by the researchers allowing them to grab, zoom, rotate and inspect multiple particles on the iPad's screen with little or no previous training.

Using the pinch gesture on the iPad, a microscopic sample can be moved up toward the viewer or down and away.

The researchers used National Instruments' LabVIEW software development environment to craft the algorithms that transmit an image of the particles being held by the tweezers to the iPad's screen, circling the particles that are currently being held, then allowing control of each using standard gestures from the Apple gesture recognition toolkit, such as pinch to zoom. The app can stream about 10 full frames per second to the iPad over WiFi showing all the separate optical traps that can currently be controlled by the tweezers. The researchers crafted multi-particle-specific gestures to simplify complex multi-particle control tasks, such as double-tapping with multiple fingers to trap and manipulate an oblong-shaped object with a multiplexed laser beam.

Using a multitouch gesture, two fingers can rotate a microscopic sample on the iPad used as a controller.

The iPad's wireless connection to the PC that actually controls the optical tweezers also removes another long-standing problem that usually requires the operator to suit up to prevent contamination of samples. However, by remotely controlling the PC interface to the holographic optical tweezers using a WiFi connection to the iPad, the operator can reside outside the clean-room conditions where the samples are actually inspected.

Apple iPhone and iPad owners can try out the interface to the iTweezer app without having to own actual holographic optical tweezers by downloading iHologram, which manipulates virtual particles but recognizes the same control gestures.